Your golf club moves in a circular arc around your body. Like any circle, your swing needs a radius. The shaft provides part of the radius. Your lead arm -- the left arm for right-handed players -- provides the other part. Keeping your lead arm straight will help you maintain the width of your arc for improved power and consistency.
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Take the club straight back from the ball in a low and slow fashion for as long as possible. Two-time British Open champion Greg Norman concentrates on moving his left elbow straight back from the ball for as long as possible. He uses this key to help create wide arc. Focusing on wide backswing will help you maintain good extension in your left arm.
Focus on maintaining good width with your rear arm as well as your leading arm. LPGA instructor Maria Palozola notes that in many cases the left arm doesn't bend on its own. The right arm often pulls the left arm in and causes the lead arm to bend or collapse. She says you should feel like your lead arm pushes the trail arm on the backswing. She advises golfers not to think so much about swinging the club up as swinging the club back and out.
Extend your hands away from your right ear at the top of your backswing. A wide gap will assure that you maintain a wide arc and keep your left arm straight all the way to the top of your backswing.
Maintain a straight left arm position as you swing down. If your left arm bends during the downswing, you are probably overusing your upper body. Your swing will lose its radius, and you will hit thin and topped shots. Start your downswing by shifting your weight onto your front foot and rotating your hips toward the target.
Stretches and Drills
Prevent left arm breakdown by increasing your flexibility in your left arm and shoulder. Reach your left arm across your chest so that forearm crosses your sternum and your arm is parallel to the ground. Grasp your left arm at the elbow or along the forearm with your right hand and pull your left arm closer to your torso. Feel the stretch in the back or your left arm and your shoulder. Hold for 30 seconds.
Feel a wide arc by holding a club in your right arm only and swinging to the top of your backswing. Check your hand position to make sure you have a wide gap between your right hand and your ear, then swing your left arm up and grip the club. Your left arm should be straight. PGA instructor Rick Smith uses this drill to teach students proper extension at the top of the swing.
Learn to extend your left arm at the top with another Rick Smith drill. Take an address position with a 5-iron. Hold the grip and let the shaft rest on your right shoulder with blade pointing behind you. Turn your shoulders until your back faces the target and extend your left arm toward the sky. Smith says that is how your left arm should feel at the top of your swing.